This paper investigates the significance of the emperor Caligula’s alleged declaration that a man ought to be either frugal or Caesar (Suet. Cal. 37.1). It argues that he probably made it once at a feast, that its humour lies in the ironic application of the term ‘frugal’ to the target of this joke, and that the target of his joke was likely Servius Asinius Celer, suffect consul in AD 38, after he had become notorious for paying an excessive price for a surmullet.